Spark plugs and methods of producing same



July 24, 1962 H. G. SCHURECHT 3,046,328

SPARK PLUGS AND METHODS OF PRODUCING SAME Filed July 20, 1959 INVENTOR.HARRY G. SCHURECHT F153- 6 mg ATTORNEYS ie f This invention relates tospark plugs, and, more particularly, to spark plugs containing animproved, confined, electrically conducting, vitreous sealing means, andto a method for producing such spark plugs.

It has heretofore been proposed to seal the center bore inwhich thecenter electrode of a spark plug is disposed by fusing a layer ofpulverized glass in the annular space between the electrodeand the bore,or above a lower section of the center electrode, and, in the lattercase, to make the seal of electrically conductive material.

In producing such known constructions, the parts to be sealed areusually assembled with the sealing material either in the form of alayer or mass of powdered glass with metal or other powders added, orwith the composite sealing material in the form of 'a pellet. Thematerial is then sufficiently softened by heating and the parts arebrought into-their final position by forcing an upper terminal electrodesection into place against or through the molten glassy material. It isapparent that such a method requires individual heating of each sparkplug and makes impossible the production of spark plugs on a mass scaleby a method in which the formation of the seal by melting of the glassymaterial takes place during the passage of an assembled unit through afurnace. The seal produced by a method in which the glass is pressedwhile molten is a dense, inflexible mass which functions well as a sealonly if no significant difference exists in the absolute'thermalexpansion of the seal parts.

In addition, the glassy material commonly employed in knownconstructions sometimes exhibits a tendency to boil out during theheating step when not confined and it has been proposed to reduce thistendency by adding to the glass a portion of the material of which thespark plug insulator is made, such material being finely powdered priorto its addition. Other attempts have been made to confine the glasssealing material during the melting step with all of the parts disposedin their final position, but'these attempts have required the formationof screw threads within the insulator bore and have otherwise beencumbersome and expensive.

In a copending application, Serial No. 447,792, of Harry GQ Schurecht,now United States Patent No. 2,898,395, a spark plug assembly isdisclosed in which the vitreous sealing means is composed of a materialwhich expands into a vesicular structure upon heating and occupies,after cooling, a volume greater than before such heating. It has beenfound that such a seal is flexible, having pockets of gas distributedtherethrough, and that the pockets," because the gas is capable ofcontraction and expansion, serve, in essence, to cushion stresses towhich the seal is subjected in service. Ordinarily, such stresses resultfrom differences in coeflicient of thermal expansion of the sealingmaterial "itself and of associated metallic and ceramic parts. The poresof the seal are, of course, separated by walls of the sealing materialso that gas leakage from one end of the seal to the other is prevented.

In producing such structures as are disclosed in the above mentionedapplication, it is essential that the expansible sealing material be atleast partially confined during the heating step due to the inherentpropensity of such a sealing material to foam and boil during the timethat it is heated in producing a seal. 7 Unless confined, the

States PatentQ ice resulting seal may be of such high porosity that itleaks because a continuous path of bubbles has formed, and remains afterhardening of the seal, or may actually boil from the space to be sealed.The confinementcan be by a tamped layer of refractory metals or metaloxides, or mixtures thereof, or by a separate cup-shaped metal member asdisclosed in the said Patent No. 2,898,395. The confinement has twodistinct advantages, namely, of overcoming the tendency to foam andboil, and of increasing the capability of a sealing material to wet themetal of the electrode parts, but the pressure on the seal material isnot suificient to produce an undesirably dense, inflexible seal, such asresults in the known processes previously described from the applicationof high mechanical pressure.

It has now been discovered, and the instant invention is based upon suchdiscovery, that excellent spark plugs can be produced on a mass scaleduring the passage of an assembled unit through a furnace when utilizingan expansible, electrically conducting, vitreous sealing materialtherein by providing at least one frictionally anchored electrode partin the insulator bore. More particularly, theinstant invention providesa method which comprises seating a first electrode part in a centralbore of a spark plug insulator, inserting a quantity of the expansiblesealing material into the bore, and then urging a second electrode partinto the insulator bore and into a predetermined position where it isfrictionally anchored relative to the insulator with at least a portionof the said sealing material being confined between, and in contactwith, each of the electrode parts, so that upon heating the sealingmaterial to a temperature sufficient to cause its expansion, it ispressed into sealing relationship with the insulator bore and uponcooling, is effective to prevent the flow of a gas therethrough.

It has been found that a frictionally anchored electrode part in thebore serves as a packing or confining member for the glass sealingmaterial, and, further, can eliminate the need for threading aninsulator and an electrode part since the frictional engagement preventssuch electrode part from being moved by. the boiling and expansion ofthe vitreous sealing material. Not only is such an assembly inexpensiveto manufacture, but, also, there are various other significantadvantages. For example, since the portion of the insulator infrictional engagement with the electrode part is held in compressiontherewith, such portion of the insulator is more resistant to impact.Further, assembly of the spark plug parts is made simpler as the glasssealing material, e.g., in the form of a pellet, is upset as a result ofthe force exerted thereon by the urging of the second electrode partinto frictional engagement with the insulator bore, thus eliminating theneed for a separate tamping operation to upset the pellet. The sealproduced is fine grained but is a porous or vesicular structure inwhichessentially all voids are surrounded completely by an adequate layer ofa homogenous, strong material. As a result of the vesicular structure,or closed porosity, the seal is sufficiently flexible to yield withoutrupture under the stress caused in service by unequal thermal expansionof metallic and ceramic parts with which it is associated.

It is, therefore, an object of the invention to provide an improvedspark plug assembly.

It is a further object of the invention to provide a novel method ofretaining the glass seal within the bore of a ceramic part of a sparkplug in such a manner that the glass seal material is not displacedduring the formation of the seal, which formation takes place with theglassy material under a pressure produced only by its confinement.

Another object of the invention is to provide an expedient method forproducing spark plug seals on a mass scale in which the firing of theseal takes place during the passage of an assembled unit through afurnace.

Other objects of the invention will in part be apparent, and in partappear hereinafter.

For a better understanding of the nature of the objects of theinvention, reference should be had to the following detailed descriptionand to the attached drawings, in which:

FIG. 1 is a central vertical sectional view of an insulator and centerelectrode assembly according to the invention, including a knurled upperelectrode part;

FIG. 2 is a fragmentary view in elevation of a modified form of an upperelectrode confining means for use in producing an assembly according tothe invention; and

FIG. 3 is a central vertical sectional View of an insulator andelectrode assembly according to the invention for use in an auxiliarygap spark plug.

Referring now to FIG. 1 of the drawings, reference numeral indicates aceramic insulator having a longitudinal bore 11 extending therethrough.The bore is provided with an internal shoulder 12 adjacent the lower endof the insulator to provide a seat for a lower, nickel sparkingelectrode part 13. An upper or terminal electrode part 14 of cold rolledsteel is positioned in the upper insulator bore and provided with ashoulder 15 limiting the extent of insertion of the electrode part intothe bore, and a raised portion comprising a vertical knurl 1 6. Thevarious projections provided on the electrode part 14 by the knurl 16effect a plurality of frictional supports whereby the electrode contactsthe surfaces of the bore and becomes firmly anchored therein.

The lower end of the upper electrode part 14 is provided with grooves asindicated at 17 in order to better anchor the upper electrode in theglassy material and make it more resistant to any torque produced bytightening a stud screw 18, in the instance where a separate, threadedstud screw is employed.

An expanded, electrically conducting vitreous sealing materialconsisting of 82.5 parts by weight of a Glass A, 1 12.5 parts by weightof aluminum metal powder, 3 parts by Weight of Tennessee ball clay, 3.0parts by weight of bentonite, and 0.5 part by weight of graphite, andindicated at 19 is disposed generally between the electrode parts 13 and14 and in contact therewith. The expanded sealing material is confinedin its desired position in the insulator bore 11 by the lower electrodepart 13, and the upper electrode part 14, and pressed, by its expansion,into sealing relationship with the insulator bore 11 thereby acting toprevent a flow of a gas therethrough. The clearance between the upperelectrode part 14 and the bore 11 is held to fairly close tolerancesince no holding powder or other additional confining means is utilized.

The terms percent and parts are used herein, and in the appended claims,to refer to percent and parts by weight, unless otherwise indicated.

A modified upper electrode structure is shown in FIG. 2. In thisstructure, the upper electrode part 20 is provided with threads 21 atthe top thereof in order that it may receive a threaded stud washer 22and stud (not shown). The remainder of the upper electrode part isconstructed in substantially the same manner as that shown in FIG. 1,with a vertical knurl 23 being provided beneath the threads 21 and aknurl 24 being provided on the lower end of the upper electrode part 20.

1 Glass A has the following composition:

Percent Ppo 30.19

Glass A has an ignition loss of 0.04:%.

In addition,

The advantages of this upper electrode structure will be subsequentlyexplained in more detail.

Referring now to FIG. 3, the auxiliary gap assembly illustrated thereinemploying the frictional engagement confining means in accordance withthe invention comprises a ceramic insulator 25 having a longitudinalbore 26 extending therethrough. The bore is provided with an internalshoulder 27 adjacent the lower end of the insulator 25 to effect a seatfor a nickel, lower sparking electrode part 28. A center electrode part29 is positioned in the insulator bore 26 and provided with a raisedportion comprising a diagonal knurl 30. The various projections providedon the surface of the electrode part 29 by the knurl 30 provide aplurality of frictional supports whereby the said electrode part 29contacts the surfaces of the bore 26 and becomes firmly anchoredtherein.

An expanded electrically conducting, vitreous sealing material of thesame composition as that employed in the assembly illustrated in FIG. 1,and indicated at 31, is disposed generally between the electrode parts258 and and in contact therewith. The expanded sealing material 31 isconfined in its desired position in the insulator bore 26 by the lowerelectrode part 28 and the center electrode part 29, and pressed by itsexpansion into sealing relationship with the insulator bore 26, therebyacting to prevent the flow of a gas therethrough. As in the assemblydisclosed in FIG. 1, the clearance between the electrode part 29 and thebore 26 is held to fairly close tolerances since no holding powder orother additional confining means is utilized.

An upper or terminal electrode part 32 is positioned in the upperinsulator bore and provided with a shoulder 33 to limit the extent ofits insertion into the bore, and to provide a predetermined spacing orgap between the upper projection of the center electrode 29 and thelower projection of the electrode part 32. A suitable knurl 34 isprovided on the electrode part 32, the projections of which contact thesurface of the bore 26 and anchor the part 32 therein. The upper orterminal electrode part 32 also includes a cylindrical, pro-formed glassseal 35 having a central cylindrical opening therein, which pre-formedseal is held in position surrounding a portion of the length of theelectrode part 32 by any suitable means, such as a nut 36. Thecomposition of the pre-formed glass seal may suitably consist, forexample,

of 60 parts of Glass A, 40 parts of alumina and 3 parts of betonite.

The vitreous sealing material employed in accordance with the inventionis, as previously mentioned, one which expands into a vesicularstructure upon heating and occupies, after cooling, a volume greaterthan before such heating. Such glass sealing material may comprisepowdered glass in admixture with an infusible substance insoluble insaid glass. For example, excellent results have been obtained by usingthe following compositions as glass seals in addition to the compositionpreviously mentioned and employed in the assemblies of FIGS. 1 and 3:

In addition to Glass A, various other glass compositions may besuccessfully employed in the vitreous sealing materials. For example,excellent glass seals have been produced when utilizing, in theexpansible, sealing composition, a glass consisting of 74.37 percentPbO, 3.77 percent SiO 8.89 percent A1 0 and 9.72 percent B 0 said glasshaving an ignition loss of 3.25 percent. A further glass compositionthat has been successfully employed in producing expansible,electrically conducting seals consists of 66.6 percent of PbO, 23.5percent of SiO 2.9 percent of A1 0 and 7.0 percent of B 0 Numerous andvarious other vitreous compositions exhibit the property of beingexpanded upon heating and occupying, after cooling, a volume greaterthan prior to such heating, and the above examples of specificcompositions are in no way intended to be limitative thereof. In thisrespect, reference may be had to the previously mentioned copendingapplication for further examples of suitable, expansible, electricallyconducting glass sealing compositions.

The lower or sparking electrode part of spark plug assemblies producedin accordance with the instant invention should be made of a metal ormetal alloy, having good high temperature and corrosion resistance. Forexample, in addition to the use of nickel as the sparking electrodepart, excellent results have been obtained with the use of nickel-ironalloys and nickel-manganese alloys.

The raised area or knurl provided on the upper electrode part, and inaddition provided on the central electrode part in an auxiliary gapassembly, may be made at any desired position on the electrode part thatextends into the insulator bore. However, since the upper portion of theinsulator is more apt to be subjected to impact than the lower portionthereof, and since frictional engagement of the upper electrode part,with the upper portion of the insulator is more likely to pre-stresssuch upper portion of the insulator and thereby increase its resistanceto impact, the best results have been obtained when the knurl isconstructed at the upper end of the upper electrode part.

To effectively anchor the upper electrode and center electrode parts inthe insulator bore in order to prevent them from being forced up by theboiling and expansion of the glass sealing material, the diameter of theraised portion or knurl is preferably constructed approximately 0.002inch to 0.005 inch larger than that of the insulator bore. Excellentresults have been obtained when employing a knurl having a diameter of0.157 inch with an insulator having a bore diameter of 0.153 inch.

The lower end of the upper electrode part in a conventional assembly,such as shown in FIG. 1, and the lower end of the center electrode partin an auxiliary gap assembly, such as shown in FIG. 3, are preferably,but not necessarily, provided with a roughened surface such as a seriesof grooves, threads, a knurl or the like, in order to better anchor theelectrodes in the glassy material. In addition, in the case of theconventional assembly, the roughened surface also provides an excellentresistance to any torque produced by tightening the stud screw in theinstance where a separate stud screw is employed. If desired, the knurl,grooves, or threads may be made to slightly overlap the lower diametersof the said electrode parts and thus also serve to provide an evensmaller clearance between the insulator bore and the electrode part atthat point. In this respect, it is again noted that the clearancebetween the upper or central electrode part and the bore of theinsulator must be held to fairly close tolerance in the absence ofholding powder or other additional confining means. If the clearance istoo great, the glass sealing material, upon heating thereof, may boil upinto the upper bore causing the glass seal to become honeycombed and.thus leak. Preferably, this clearance is held to a maximum of 0.007inch. Excellent results have been obtained when using an electrode parthaving a diameter of 0.148 inch to 0.150 inch in an insulator bore of0.153 inch diameter. The upper or terminal electrode part is preferablymade of cold rolled steel or other good heat conducting material.

In producing a spark plug assembly, such as illustrated in FIG. 1, a.lower electrode part 13 is first inserted into the insulator bore 11 andseated on the shoulder 12 provided therein. A predetermined quantity ofglass sealing material 19 of the desired composition, either in powderform or pellet form, is next inserted into the bore. The upper electrodepart 14 is then inserted in the bore and force is applied thereto toadvance the raised portion or knurling 16 to enter the bore therebyanchoring the upper electrode part therein. In this respect, it shouldbe noted that the pressure applied to the upper electrode part should begreat enough to thoroughly tamp the sealing material into place.Therefore, if greater force is required to accomplish suflicient tampingor upsetting of the sealing material than is necessary to force theknurling into the insulator bore, such greater force must be applied.Generally, a force in the range of approximately 400 pounds to 700pounds has been found to be sufficient in this respect. After the upperelectrode part is securely in place, the assembly is then placed in asuitable furnace and heated to a temperature suflicient to at leastsoften and mature the sealing material. Generally, the maturingtemperature of the expansible, electrically conducting glass sealingcompositions employed in accordance with the invention is in the rangeof 1100 F. to 2200 F.

In producing the assembly illustrated in FIG. 1, it will be appreciatedthat care must be taken in correlating the size of the glass sealingpellet or amount of glass sealing powdered material employed, the lengthof the upper electrode part 'below the shoulder thereof, and of thediameter of the bore, with the force required to urge said upperelectrode into place and tamp and upset said sealing material. Forexample, if a pellet is not of sufficient mass, or if too little powderis provided, or if the bore is larger than usual, said pellet may notreceive the full tamping pressure and the resulting seal may leak. Onthe other hand, if the pellet consists of too great a mass or if toomuch powder is provided, or if the bore is smaller than average, theshoulder on the upper electrode part will not be flush with the top ofthe insulator causing the spark plug stud to have a weak appearance.

In order to overcome this difficulty, use can be made of the modifiedupper electrode structure illustrated in FIG. 2. When employing thisstructure, the full force on the electrode would be transmitted to theglass sealing material in all cases, even when the amount of glasssealing material varied, since the stud washer is screwed in place afterthe pressure has been applied. Further, closure contact of the studwasher and stud to the insulator would also be assured, and hence theupper portion of the insulator would be more apt to be pre-stressed andtherefore more resistant to impact.

In producing the auxiliary gap spark plug assembly illustrated in FIG.3, the lower electrode part 28 is first inserted into the insulator bore26 and seated on the shoulder provided therein. .A predetermined amountof glass sealing material 31 in powder or pellet form is then insertedinto the bore. The center electrode part 29 is then inserted into thebore and force applied thereto to advance the knurling 30 providedthereon into the bore and additionally to cause the center electrodepart to upset or tamp the pellet or powder in place. A preformed glassseal 35 is placed on the upper electrode part and held in place thereonby the nut 36 secured to the lower end of the upper electrode part 32.The electrode part 32, together with the preformed seal is then insertedinto the insulator bore and force is applied thereto to advance theknurling provided thereon into the bore and to seal the shoulder 33 ofthe electrode part 32 on the top of the insulator. After the upperelectrode part 32 is securely in place, the resulting assembly is placedin a suitable furnace and heated to a temperature suflicient to softenand mature the sealing material. The assembly is then removed from theoven and allowed'to cool.

The following example constitutes the best presently known mode forpracticing the instant invention and describes the formulation of asuitable, expansible, electrically conducting, vitreous sealing means,and the construction and method of assembly of the various partsemployed in producing a spark plug in accordance with the invention.

Example Parts Glass A 77.5 Aluminum metal powder 17.5 Tenn. ball clay3.0 Bentonite 2.0 Graphite 0.5

An upper electrode part such as shown in FIG. 2, having a major diameterof 0.150 inch and a rectangular, cross sectional shaped projection atthe lower end thereof approximately 0.0875 inch by 0.061 inch and 0.125inch in length was then inserted in the insulator bore. The electrodepart was knurled at its upper end just beneath the threads, theprojections of the knurl extending outwardly from the electrode partapproximately 0.007 inch. A force of 500 pounds was applied to the upperelectrode part, a later section of the completed assembly showing suchpressure produced a gap of approximately 0.1875 inch between the upperlob of the lower electrode and the bottom of the projection on the upperelectrode.

A stud washer was then applied to the threaded end of the upperelectrode and screwed doWn until it was flush with the insulator. A studscrew was then threaded on the upper electrode to complete the assembly.

The resulting assembly was then placed in a furnace previously heated tol450 F.; the furnace was allowed to come back to temperature; and theassembly was held at such temperature for minutes and was then removedfrom the furnace and allowed to cool.

Upon testing the assembly, it was found that the seal was completely gastight under operating conditions, there being no leak when the assemblywas subjected to a 1000 psi. leakage test. By visual examination of thesectioned seal, it was found that the seal exhibited the requisiteexpansion, and was vesicular in structure.

It will be appreciated that the present invention provides a spark plugassembly in which the sealing material is prevented from foaming orboiling out while the seal is being fired, and in which the confinementof the sealing material by the firmly anchored upper electrode partcauses an internal pressure which promotes wetting of the metalelectrode parts and of the ceramic insulator by the glassy material.Further, the assembly employed in accordance with the invention makespossible the mass scale production of spark plugs in which an expandedvesicular, flexible seal is formed by melting of the glassy materialduring the passage of an assembled unit through a furnace.

While the foregoing description is considered to be of the moreadvantageous embodiments of the invention, it is obvious that manymodifications and variations can he made in the compositions andspecific procedures discussed without departing from the spirit andscope of the present invention, as those skilled in the art will readilyunderstand. Such modifications and variations are considered to bewithin the purview and scope of the inven tion as defined by theappended claims.

This application is a continuation-in-part of co-pending applicationSerial No. 447,792, filed August 4, 1954, now Patent No. 2,898,395.

I claim:

1. In a spark plug assembly, an insulator having a firing end and aterminal end, and having a central bore extending thorethrough, a firstelectrode part seated in the bore of said insulator, a second electrodepart spaced axially in said bore from said first electrode part,anchoring means on second electrode part comprising a plurality ofspaced, discontinuous, outwardly extending circumferential projections,the radii of which are greater than the radius of the insulator borewhereby said projections frictionally engage said insulator bore andanchor the second electrode part relative thereto, and an expanded,substantially gas-impervious, electrically conducting, vitreous sealingmeans disposed in at least a part of the insulator bore substantiallyfilling the portion of the bore between, and in contact with each of,said electrode parts, said vitreous sealing means being vesicular instructure, and pressed by its expansion into sealing relationship withthe insulator bore, and effective to prevent the flow of a gastherethrough.

2. In a spark plug assembly, an insulator having a central bore, anelectrode element extending axially through the bore and comprising aterminal end part and a separate, axially spaced sparking end part, eachof said parts having an outer end externally of the bore, anchoringmeans on at least a portion of the terminal end part exending into theinsulator bore comprising a plurality of spaced, discontinuous,outwardly extending circumferential projections, the radii of which aregreater than the radius of the insulator bore whereby said projectionsfricionally engage said insulator bore and anchor the terminal end partrelative thereto, and an expanded, substantially gas-impervious,electrically conducting, vitreous sealing means disposed in at least apart of the insulator bore substantially filling the portion of the borebetween, and in contact with both, said electrode parts, said vitreoussealing means being vesicular in structure and pressed by its expansioninto sealing relationship with the insulator bore, and effective toprevent the flow of a gas therethrough.

3. A method of sealing the bore of a spark plug insulator and assemblingan electrode therein, which comprises, seating a first electrode part ina central bore of an insulator, inserting a quantity of a vitreoussealing material into the insulator bore, said sealing material beingone which, when heated, expands into a vesicular, electricallyconducting structure and occupies, upon cooling, a volume greater thanbefore such heating, urging a second electrode part into the insulatorbore and into a position where it is frictionally anchored to theinsulator, with at least a portion of said vitreous sealing materialconfined between and in contact with each. of said electrode parts, andthen heating at least the vitreous sealing material to a temperaturesufficient to cause the expansion thereof into a vesicular, electricallyconducting structure, whereby said vitreous sealing material is pressed,by its expansion, into sealing relationship with the insulator bore andis effective to prevent the flow of a gas therethrough while said secondelectrical part remains in its said position.

4. A method of sealing the bore of a spark plug insulator and assemblingan electrode therein, which comprises, seating a first electrode part ina central bore of an insulator, inserting a quantity of a vitreoussealing material into the insulator bore, said sealing material beingone which, when heated, expands into a vesicular, electricallyconducting structure and occupies, upon cooling, a volume greater thanbefore such heating, urging a second electrode part into the insulatorbore and into a position where it is frictionally anchored to theinsulator, with. at least a portion of said vitreous sealing materialconfined between and in contact with each of said electrode parts,urging a third electrode part into the insulator bore and into aposition where it is frictionally anchored to the insulator but isspaced longitudinally a predetermined distance from the second electrodepart and then heating at least the vitreous sealing material to 'atemperature sufiicient to cause the expansion thereof into a vesicular,electrically conducting structure, whereby said vitreous sealingmaterial is pressed, by its expansion, into sealing relationship withthe insulator bore and is effective to prevent the flow of a gastherethrough While said second electrode part remains in its saidposition.

- References Cited in the file of this patent UNITED STATES PATENTSSchwartzwalder et al Jan. 25, 1938 Cipriani July 31, 1945 Candelise eta1 June 24, 1958 Pierce Feb. 17, 1959 Schurecht Aug. 4, 1959

